On starting of a new game the base entrance is blocked by rocks/boulders which are not frobbable / clearable.
The existing rock formations outside the base should be frobbable (the imp robots should able to break/remove them at least).
They could behave like normal solid rock cubes from the base, by yielding either a fossil / a resource or nothing.
They may leave behind smaller (passable) rocks for esthetic reasons.

The outside/non room environment permits deploying of shaped charge to eliminate the rocks. I still think breaking them down the normal way should be available also.
In any case, the rocks exactly in front of the airlock entrance should not be there. How would have the colonists arrived in the base ?